Downtown 250i cold start issue

[scooterfan]

Time for an update!


Will definitely talk to the mechanics about the valve clearance and will let you know. Sorry for the (maybe stupid) question but how does a valve clearance issue affect the engine startup only when cold?

Thanks

Yannick



Let me explain the other way round - valve lashes which are too small normally cause “hot start” problems (not “cold start”problems). The reasons are as follows :

 When the engine is cold and there is no lash between a valve stem rocker arm and the rocker arm is j-u-s-t touching the valve stem, the valve will still be closing completely and the engine should start easily when cold.

But when the engine heats up heat expansion takes place and the valve stem will start stretching slightly. When the valve stem starts stretching, the valve will not close properly and will start leaking. Which means:
1. Engine compression will start dropping.
2. A mixture of exhaust fumes and gasoline will be sucked into the combustion chamber.
3. Air / fuel mixture inside the combustion chamber will be incorrect.

Therefore it becomes difficult to start the engine when it is hot - the valve stem will still be slightly stretched and the valve will still not seal properly.
But when the engine cools down again -the valve stem will “crimp” again, the valve will seal again, and the engine will start easily.

You seem to find yourself in a warmer climate, and the lash between your scooter’s rocker arm and valve stems might be right on the edge (zero) - which means the engine might still behave quite strange in a “not so cold” climate when the engine never actually gets that “cold”.

Having said all this -if the lash on your rocker / valves are about zero at the moment, you should also experience a starting problem after a ride - when the engine is still hot. Therefore my initial comment “ your ‘cold start’ problem doesn’t sound like a typical cold start problem but...........”

[Viper254]

Hi Yannick,

It shouldn't - poor valve clearances are usually associated with hot engines, where the slight expansion of the valve means it doesn't seat properly and compression is reduced.

[YUL713]

Hi Yannick,

It shouldn't - poor valve clearances are usually associated with hot engines, where the slight expansion of the valve means it doesn't seat properly and compression is reduced.

Thanks 

[Stig / Major Tom]

Hi Yannick,

It shouldn't - poor valve clearances are usually associated with hot engines, where the slight expansion of the valve means it doesn't seat properly and compression is reduced.

Not to contest your thinking - but time and again I've read that many do not check the valves until the scooter becomes hard to start. That is how long so many PCX owners wait - and it is how long they're told to wait by their forum gurus. "Leave the valves alone until it becomes hard to start." (a PCX is a pain to get to the valves!)

Stig

[YUL713]

If ever that can help, here are 2 engine starts, the "hot" one just after a 30Km commute this afternoon and the "cold" one after a 2 hours rest! Speaks for itself...

[YUL713]

COLD one now

[CROSSBOLT]

Rats! Won't play! Where are you? I'll be right over!

[YUL713]

Here we go again:

HOT :

COLD :

[Stig / Major Tom]

Here we go again:

HOT :

COLD :

Starts hot and cold?
So, it healed itself....or, what?
Cool dash!
Stig

[scooterfan]

Starts hot and cold?
So, it healed itself....or, what?
Cool dash!
Stig

To my understanding from Stig's response the videos actually shows "pretty normal" results about engine behavior on Kymcos with EFI systems. Maybe other owners with EFI scooters should confirm ?

I think this rather looks like a possible fuel supply / air mixture "problem"  though.

I just did a quick Google search, and stumbled across some info which is actually not Kymco related :

https://mechanics.stackexchange.com/questions/5643/motorcycle-with-efi-not-starting-well

Looks like you should also get the battery tested, or maybe you need a diagnostic tool to solve the problem.

If the agents are not able or willing to do anything about this, I guess you need to live with the scooter as is - or you need to trade the scooter on a carburetor model.

[Stig / Major Tom]

Not visible in the video. ....are you touching the throttle when starting?
EFI is a "hands off" start,  in 99% of all situations. Scoots and autos.
Maybe a heartbeat or two longer wait before using start button. Give all systems a chance to get fully pants-ed for their days work! (Although, most EFI systems are even American Driver  Proof....😊)
Stig

[CROSSBOLT]

Hot start = no compression
Cold start =  normal compression
My conclusion: first suspect is valve clearances too small.

[scooterfan]

Here we go again:

HOT :

COLD :

 Something doesn't look right.  By comparing the two rev counters on the two videos, it looks like after a "cold start" the engine Rpm's are lower just after the engine started - then the Rpm's start creeping higher after a few seconds.
I think this might point at a pressure problem in the fuel line, (i.e. dirty fuel filter, faulty pressure relieve valve, faulty fuel pump, etc) or faulty sensors in the EFI system.

Another question which might be important :  What was the ambient temperature during the two tests on the video ?
Maybe this is a Choke-related problem ?

[CROSSBOLT]

I was going by the hot start cranking sound: very fast with very little if any variation. The cold crank was like my almost broken in DT300i two turns and run. Good videos on utube by the way!

[stuo]

Starting a cold engine requires more fuel, less air, which is why we had chokes on old carburetor engines and a cold start circuit on modern EFI engines. I suspect there is a cold start injector or enrichener on your scooter engine that is not working properly.